ADS16axx Reference Options
1
Introduction
The ADS1605, ADS1606 and ADS1625, ADS1626 can operate from an internal or external voltage reference. In either case, the reference voltage VREF is set by the differential voltage between VREFN and VREFP: VREF = (VREFP – VREFN). VREFP and VREFN each use two pins, which should be shorted together. VMID equals approximately 2.5 V and is used by the modulator. VCAP connects to an internal node and must also be bypassed with an external capacitor. For the best analog performance, it is recommended that an external reference voltage (VREF) of 3 V be used.
Internal Reference
To use the internal reference, set the REFEN pin low. This activates the internal circuitry that generates the reference voltages. The internal reference voltages are applied to the pins. Good bypassing of the reference pins is critical to achieve optimum performance and is done by placing the bypass capacitors as close to the pins as possible. Figure 2-1 shows the recommended bypass capacitor values. Use high quality ceramic capacitors for the smaller values. Avoid loading the internal reference with external circuitry. If the ADS1605, ADS1606 or ADS1625, ADS1626 internal reference is to be used by other circuitry, buffer the reference voltages to prevent directly loading the reference pins.
Figure 2-1 Internal Reference Bypassing